The present invention relates generally to endoscopes and, more particularly, to a guide tube assembly of an endoscope, for guiding an elongated operating instrument or the like, for example.
A usual or general endoscope comprises an operating body and a flexible inserting portion extending therefrom. The inserting portion has a distal end section serving as a yieldable or bendable section which can be curved by remote-operation at the operating body. A distal end of the bendable section is formed into a relatively hard tip component. Received within the inserting portion is a guide tube for guiding an elongated operating instrument or the like. The operating instrument is inserted from a proximal opening provided in the operating body, passes through the guide tube, and is led in a body cavity or coelom through a distal opening provided in the tip component, so that the operating instrument can tear off some tissues from the inner wall of the body cavity, for example.
The guide tube is required to have low coefficient of friction, in order to permit the operating instrument to be smoothly inserted and withdrawn. In addition, the guide tube is required to have low bending resistance, in order to facilitate the bending operation of the bendable section. Moreover, the guide tube is also required to be curved in a round fashion when the bendable section is bent, such that the cross-sectional shape of the guide tube is maintained substantially circular at the curved region. The reason for this is that, should the guide tube be folded in an acute angle and the cross-sectional shape thereof be crushed, it would become impossible to guide the operating instrument.
Drawn, porous tetrafluoroethylene resin is often used as a material of the guide tube which satisfies the above requirements.
Since the guide tube formed of the porous tetrafluoroethylene resin has repellency, usual water having high surface tension cannot pass through the minute or fine pores of the peripheral wall of the guide tube. However, humor or the like having low surface tension can be permeated into the pores. For this reason, measures are taken to apply fluoro rubber to an inner or an outer peripheral surface of the guide tube so as to partially impregnate the peripheral wall thereof with the fluoro rubber, to thereby prevent the humor from leaking through the pores, as has been proposed in, for example, Japanese Utility Model Laid-Open Application Nos. 54-115184 and 54-115185.
With the construction described above, however, the bending resistance of the guide tube increases, because the peripheral wall thereof is impregnated with the rubber such that the coating is integrally formed on the inner or outer peripheral surface. This reduces the advantage of the porous tetrafluoroethylene resin.
In particular, if the outer peripheral surface of the guide tube is coated with the rubber, bacterial tend to propagate within the pores, because the humor penetrates into the pores until it reaches the rubber coating. For this reason, it is necessary to sterilize or disinfect the guide tube after use of the endoscope. However, the conventional construction has the following problems.
The case where disinfecting liquid is employed will first be described in detail. As the disinfecting liquid passes through the guide tube, the disinfecting liquid is permeated into the pores of the peripheral wall of the guide tube. However, the pores are closed at their respective outer ends by the rubber coating and, therefore, the disinfecting liquid cannot reach the bottoms of the respective pores. This makes it difficult to effect sufficient or complete disinfection. Moreover, after the disinfection, the inner tube is rinsed with water and is dried, but sufficient drying cannot be effected because the outer ends of the respective pores are closed. The fluid remains at the bottoms of the respective pores. Thus, bacterial might again propagate.
In case of employment of disinfecting gas, the endoscope is first washed with usual water. However, since the pores are closed at their respective outer ends, no sufficient water reaches the bottoms of the respective pores so that the washing cannot be effected in a reliable manner. In addition, after the washing, the endoscope is disposed within a chamber which is under vacuum, to remove air and water from the interior of the endoscope. Subsequently, the endoscope is disinfected with the disinfecting gas. However, since a part of the liquid such as humor, washing water and the like remains at the bottoms of the respective pores, it is not possible to achieve sufficient sterilization due to the disinfecting gas.
Japanese Utility Model Laid-Open Application Nos. 52-90990 and 57-7502 disclose a guide tube assembly of double tube structure. The inner tube of the former application is formed by a helically wound metallic wire, but is not formed of porous resin as is in the present invention. The inner tube of the latter application is formed of porous resin, but the inner and outer tubes do not define therebetween an annular region or space through which fluid can flow.